Trigger profile for a power tool

ABSTRACT

An improved method is provided for operating a power tool. The method includes receiving an input control variable from an input unit; determining a derivative of the input control variable; selecting one of a plurality of control profiles based on the control input variable and the derivative, each control profile correlating the control input variable of the input unit to a rotational speed at which to drive the output shaft; and driving the output shaft at a rotational speed in accordance with the selected control profile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/404,620 filed on Feb. 24, 2012, which is acontinuation-in-part of U.S. patent application Ser. No. 13/120,873filed on May 13, 2011, which is a national phase of PCT/US2011/020511filed Jan. 7, 2011, which claims the benefit of U.S. ProvisionalApplication Nos. 61/292,966, filed on Jan. 7, 2010, and 61/389,866,filed on Oct. 5, 2010. The entire disclosures of each of the aboveapplications are incorporated herein by reference.

FIELD

The present disclosure relates generally to power tools, such as a powerscrewdriver, and, more particularly, to a control scheme that controlsrotation of an output member of a tool based on a user input.

BACKGROUND

In present-day power tools, users may control tool output through theuse of an input switch. This can be in the form of a digital switch inwhich the user turns the tool on with full output by pressing a buttonand turns the tool off by releasing the button. More commonly, it is inthe form of an analog trigger switch in which the power delivered to thetool's motor is a function of trigger travel. In both of theseconfigurations, the user grips the tool and uses one or more fingers toactuate the switch. The user's finger must travel linearly along oneaxis to control a rotational motion about a different axis. This makesit difficult for the user to directly compare trigger travel to outputrotation and to make quick speed adjustments for finer control.

Another issue with this control method is the difficulty in assessingjoint tightness. As a joint becomes tighter, the fastener becomes morereluctant to move farther into the material. Because the tool motorattempts to continue spinning while the output member slows down, areactionary torque can be felt in the user's wrist as the user increasesbias force in an attempt to keep the power tool stationary. In thiscurrent arrangement, the user must first sense tightness with the wristbefore making the appropriate control adjustment with the finger.

This section provides background information related to the presentdisclosure which is not necessarily prior art.

SUMMARY

An improved method is provided for operating a power tool. The methodincludes: receiving an input control variable from an input unit;determining a derivative of the input control variable; selecting one ofa plurality of control profiles based on the control input variable andthe derivative, each control profile correlating the control inputvariable of the input unit to a rotational speed at which to drive theoutput shaft; and driving the output shaft at a rotational speed inaccordance with the selected control profile.

In an embodiment, the method includes selecting a first control profilefrom the plurality of control profiles when the derivative of thecontrol input variable is above a first threshold and selecting a secondcontrol profile from the plurality of control profiles when thederivative of the control input variable is below the first threshold,where the first control profile differs from the second control profile.In an embodiment, the first control profile designates maximumrotational speed of the output shaft for a predetermined range of thecorresponding control input variable and the second control profiledesignates a linear control relationship between the rotational speed ofthe output shaft and the corresponding control input variable.

In a further embodiment, the method includes selecting a third controlprofile from the plurality of control profiles when the variable of thecontrol input variable is below a second threshold below the firstthreshold. The third control profile may designate a control curvehaving a first linear curve corresponding to a first range of thecontrol input variables and a second linear curve steeper than the firstlinear curve and corresponding to a second range of control inputvariables.

According to an embodiment, the input unit includes a trigger switch andthe control input variable includes one of a displacement, velocity, oracceleration of the trigger switch. The derivative of the control inputvariable may be, for example, a speed at which the input unit isactuated.

In another embodiment, the input unit includes a rotational motionsensor disposed in the power tool and configured to measure rotationalmotion of the power tool about an axis aligned substantially parallelwith a longitudinal axis of the output shaft. The control input variablemay be an angular displacement of the tool about the axis and thederivative may be an angular velocity of the tool about the axis. Themethod may include determining the angular displacement of the toolabout the axis in relation to a reference position and driving theoutput shaft at a rotational speed that correlates to the angulardisplacement of the tool from the reference position based on theselected control profile. The reference position may be reset to zero inresponse to an input command from an operator of the tool.

According to another aspect of the invention, a power tool is provided,including a housing, an output member configured to rotate about alongitudinal axis; a motor contained in the housing and driveablyconnected to the output member to impart rotary motion thereto; an inputunit configured to output an input control variable in response to auser action; and a controller in the housing configured to calculate aderivative of the input control variable, select one of a plurality ofcontrol profiles based on the control input variable and the derivative,and drive the output shaft via the motor at a rotational speed inaccordance with the selected control profile, where each control profilecorrelating the control input variable of the input unit to a rotationalspeed at which to drive the output shaft. The controller of thisembodiment may be configured to execute one or more of the steps of themethod discussed above.

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

FIG. 1 is a perspective view of an exemplary power screwdriver;

FIG. 2 is a longitudinal section view of the power screwdriver of FIG.1;

FIG. 3 is a perspective view of the power screwdriver of FIG. 1 with thehandle being disposed in a pistol-grip position;

FIG. 4 is an exploded perspective view of the power screwdriver of FIG.1;

FIGS. 5A-5C are fragmentary section views depicting different ways ofactuating the trigger assembly of the power screwdriver of FIG. 1;

FIGS. 6A-6C are perspective views of exemplary embodiments of thetrigger assembly;

FIG. 7 is a schematic for an exemplary implementation of the powerscrewdriver;

FIGS. 8A-8C are flow charts for exemplary control schemes for the powerscrewdriver;

FIGS. 9A-9E are charts illustrating different control curves that may beemployed by the power screwdriver;

FIG. 10 is a diagram depicting an exemplary pulsing scheme for providinghaptic feedback to the tool operator;

FIG. 11 is a flow chart depicting an automated method for calibrating agyroscope residing in the power screwdriver;

FIG. 12 is a partial sectional view of the power screwdriver of FIG. 1illustrating the interface between the first and second housingportions;

FIG. 13A-13C are perspective views illustrating an exemplary lock barassembly used in the power screwdriver;

FIG. 14A-14C are partial sectional views illustrating the operation ofthe lock bar assembly during configuration of the screwdriver from the“pistol” arrangement to the “inline” arrangement;

FIG. 15 is a flowchart of an exemplary method for preventing anoscillatory state in the power screwdriver;

FIG. 16 is a fragmentary section view depicting an alternative triggerswitch assembly;

FIGS. 17A-17C are cross-sectional views illustrating alternative on/offand sensing mechanisms;

FIG. 18 is a flowchart for another exemplary control scheme for thetool;

FIGS. 19A-19B are diagrams illustrating an exemplary self-lockingplanetary gear set;

FIG. 20 is a perspective view of a second exemplary power screwdriver;

FIG. 21 is a perspective view of a third exemplary power screwdriver;

FIGS. 22A-B are cross-sectional views of the exemplary power screwdriverof FIG. 21, illustrating one way to activate the reaming tool; and

FIGS. 23A-B are cross-sectional views of the exemplary power screwdriverof FIG. 21, illustrating a second way to activate the reaming tool.

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure. Correspondingreference numerals indicate corresponding parts throughout the severalviews of the drawings.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, an exemplary power screwdriver isindicated generally by reference number 10. The screwdriver 10 iscomprised generally of an output member 11 configured to rotate about alongitudinal axis 8 and a motor 26 driveably connected to the outputmember 11 to impart rotary motions thereto. Tool operation is controlledby a trigger switch, a rotational rate sensor and a controller in amanner further described below. A chuck or some other type of toolholder may be affixed to the end of the output member 11. Furtherdetails regarding an exemplary bit holder are set forth in U.S. patentapplication Ser. No. 12/394,426 which is incorporated herein byreference. Other components needed to construct the screwdriver 10 arefurther described below. While the following description is providedwith reference to screwdriver 10, it is readily understood that thebroader aspects of the present disclosure are applicable to other typesof power tools, including but not limited to tools having elongatedhousings aligned concentrically with the output member of the tool.

The housing assembly for the screwdriver 10 is preferably furthercomprised of a first housing portion 12 and a second housing portion 14.The first housing portion 12 defines a handle for the tool and can bemounted to the second housing portion 14. The first housing portion 12is rotatable in relation to the second housing portion 14. In a firstarrangement, the first and second housing portions 12, 14 are alignedwith each other along the longitudinal axis of the tool as shown in FIG.1 This arrangement is referred to herein as an “inline” configuration.

The screwdriver 10 may be further configured into a “pistol-type”arrangement as shown in FIG. 3. This second arrangement is achieved bydepressing a rotation release mechanism 130 located in the side of thesecond housing portion 14. Upon depressing the release mechanism 130,the first housing portion 12 will rotate 180 degrees in relation to thesecond housing portion 14, thereby resulting in the “pistol-type”arrangement. In the second arrangement, the first and second housingportions 12, 14 form a concave elongated groove 6 that extends from oneside of the tool continuously around the back to the other side of thetool. By placing an index finger in the groove 6 on opposing sides, thetool operator can better grip the tool, and the positioning of the palmdirectly behind the longitudinal axis 8 allows the operator to bettercontrol the screwdriver.

With reference to FIGS. 2 and 4, the first housing portion 12 can beformed from a pair of housing shells 41, 42 that can cooperate to definean internal cavity 43. The internal cavity 43 is configured to receive arechargeable battery pack 44 comprised of one or more battery cells. Acircuit board 45 for interfacing the battery terminals with othercomponents is fixedly mounted in the internal cavity 43 of the firsthousing portion 12. The trigger switch assembly 50 is also pivotablycoupled to the first housing portion 12.

Likewise, the second housing portion 14 can be formed of a pair ofhousing shells 46, 47 that can cooperate to define another internalcavity 48. The second housing portion 14 is configured to receive thepowertrain assembly 49 which includes the motor 26, the transmission,and the output member 11. The power train assembly 49 can be mounted inthe internal cavity 48 such that a rotational axis of the output memberis disposed concentrically about the longitudinal axis of the secondhousing portion 14. One or more circuit boards 45 are also fixedlymounted in the internal cavity 48 of the second housing portion 14 (asshown in FIG. 14A). Components mounted to the circuit board may includethe rotational rate sensor 22, the microcontroller 24 as well as othercircuitry for operating the tool. The second housing portion 14 isfurther configured to support the rotation release mechanism 130.

With reference to FIGS. 3, 4, 12, 13, and 14, the rotary releasemechanism 130 can be mounted in either the first or second housingportions 12, 14. The release mechanism 130 comprises a lock bar assembly140 that engages with a set of locking features 132 associated with theother one of the first and second housing portions. In the exemplaryembodiment, the lock bar assembly 140 is slidably mounted inside thesecond housing portion 14. The lock bar assembly 140 is positionedpreferably so that it may be actuated by the thumb of a hand grippingthe first housing portion 12 of the tool. Other placements of the lockbar assembly and/or other types of lock bar assemblies are alsocontemplated. Further details regarding another lock bar assembly isfound in U.S. patent application Ser. No. 12/783,850 which was filed onMay 20, 2010 and is incorporated herein by reference.

The lock bar assembly 140 is comprised of a lock bar 142 and a biasingsystem 150. The lock bar 142 is further defined as a bar body 144, twopush members 148 and a pair of stop members 146. The push members 148are integrally formed on each end of the bar body 144. The bar body 144can be an elongated structure having a pocket 149 into which the biasingsystem 150 is received. The pocket 149 can be tailored to the particularconfiguration of the biasing system. In the exemplary embodiment, thebiasing system 150 is comprised of two pins 152 and a spring 154. Eachpin 152 is inserted into opposing ends of the spring 154 and includes anintegral collar that serves to retain the pin in the pocket. When placedinto the pocket, the other end of each pin protrudes through an apertureformed in an end of the bar body with the collar positioned between theinner wall of the pocket and the spring.

The stop members 146 are disposed on opposite sides of the bar body 144and integrally formed with the bar body 144. The stop members 146 can befurther defined as annular segments that extend outwardly from a bottomsurface of the bar body 144. In a locking position, the stop members 146are arranged to engage the set of locking features 132 that areintegrally formed on the shell assembly of the first housing portion 12as best seen in FIG. 14A. The biasing system 150 operates to bias thelock bar assembly 140 into the locking position. In this lockingposition, the engagement of the stop members 146 with the lockingfeatures 132 prevents the first housing portion from being rotated inrelation to the second housing portion.

To actuate the lock bar assembly 140, the push members 148 protrudethrough a push member aperture formed on each side of the second housingportion 14. When the lock bar assembly 140 is translated in eitherdirection by the tool operator, the stop members 146 slide out ofengagement with the locking features 132 as shown in FIG. 14B, therebyenabling the first housing portion to rotate freely in relation to thesecond housing portion. Of note, the push members 148 are offset fromthe center axis on which the first housing portion 12 and the secondhousing portion 14 rotate with respect to one another. This arrangementcreates an inertial moment that helps to rotate the second housingportion 14 in relation to the first housing portion 12. With a singleactuating force, the tool operator can release the lock bar assembly 140and continue rotating the second housing portion. The user can thencontinue to rotate the second housing portion. The user can thencontinue to rotate the second housing portion (e.g., 180 degrees) untilthe stop members re-engage the locking features. Once the stop members146 are aligned with the locking features, the biasing system 150 biasesthe lock bar assembly 140 into a locking position as shown in FIG. 14C.

An improved user-input method for the screwdriver 10 is proposed.Briefly, tool rotation is used to control rotation of the output member.In an exemplary embodiment rotational motion of the tool about thelongitudinal axis of the output member is monitored using the rotationalmotion sensor disposed in the power tool. The angular velocity, angulardisplacement, and/or direction of rotation can be measured and used as abasis for driving the output member. The resulting configurationimproves upon the shortcomings of conventional input schemes. With theproposed configuration, the control input and the resulting output occuras a rotation about the axis. This results in a highly intuitive controlsimilar to the use of a manual screwdriver. While the followingdescription describes rotation about the longitudinal axis of the outputmember, it is readily understood that the control input could berotational about a different axis associated with the tool. For example,the control input could be about an axis offset but in parallel with theaxis of the output member or even an axis askew from the axis of theoutput member. Further details regarding the control scheme may be foundin U.S. Patent Application No. 61/292,966 which was filed on Jan. 7,2010, and is incorporated herein by reference.

This type of control scheme requires the tool to know when the operatorwould like to perform work. One possible solution is a switch that thetool operator actuates to begin work. For example, the switch may be asingle pole, single throw switch accessible on the exterior of the tool.When the operator places the switch in an ON position, the tool ispowered up (i.e., battery is connected to the controller and otherelectronic components). Rotational motion is detected and acted upononly when the tool is powered up. When the operator places the switch inan OFF position, the tool is powered down and no longer operational.

In the exemplary embodiment, the tool operator actuates a trigger switchassembly 50 to initiate tool operation. With reference to FIGS. 5A-5C,the trigger switch assembly 50 is comprised primarily of an elongatedcasing 52 that houses at least one momentary switch 53 and a biasingmember 54, such as a spring. The elongated casing 52 is movably coupledto the first housing portion 12 in such a way that allows it totranslate and/or pivot about any point of contact by the operator. Forexample, if the tool operator presses near the top or bottom of theelongated casing 52, the trigger switch assembly 50 pivots as shown inFIGS. 5A and 5B, respectively. If the tool operator presses near themiddle of the elongated casing 52, the trigger switch assembly 50 istranslated inward towards the tool body as shown in FIG. 5C. In anycase, the force applied to the elongated casing 52 by the operator willdepress at least one of the switches from an OFF position to an ONposition. If there are two or more switches 53, the switches 53 arearranged electrically in parallel with each other (as shown in FIG. 7)such that only one of the switches needs to be actuated to power up thetool. When the operator releases the trigger, the biasing member 54biases the elongated casing 52 away from the tool, thereby returningeach of the switches to an OFF position. The elongated shape of thecasing helps the operator to actuate the switch from different grippositions. It is envisioned that the trigger switch assembly 50 may becomprised of more than two switches 53 and/or more than one biasingmember 54 as shown in FIGS. 6A-6C.

FIG. 16 illustrates an alternative trigger switch assembly 50, wherelike numerals refer to like parts. Elongated casing 52 is preferablycaptured by the first housing portion 12 so that it can only slide inone particular direction A. Elongated casing 52 may have ramps 52R.Ramps 52R engage cams 55R on a sliding link 55. Sliding link 55 iscaptured by the first housing portion 12 so that it can preferably onlyslide in along a direction B substantially perpendicular to direction A.

Sliding link 55 is preferably rotatably attached to rotating link 56.Rotating link 56 may be rotatably attached to the first housing portion12 via a post 56P.

Accordingly, when the user moves elongated casing 52 along direction A,ramps 52R move cams 55R (and thus sliding link 55) along direction B.This causes rotating link 56 to rotate and make contact with momentaryswitch 53, powering up the screwdriver 10.

Preferably, elongated casing 52 contacts springs 54 which bias elongatedcasing 52 in a direction opposite to direction A. Similarly, slidinglink 55 may contact springs 55S which bias sliding link 55 in adirection opposite to direction B. Also, rotating link 56 may contact aspring 56S that biases rotating link 56 away from momentary switch 53.

Persons skilled in the art will recognize that, because switch 53 can bedisposed away from elongated casing 52, motor 26 can be providedadjacent to elongated casing 52 and sliding link 55, allowing for a morecompact arrangement.

Persons skilled in the art will also recognize that, instead of havingthe user activating a discrete trigger assembly 50 in order to power upscrewdriver 10, screwdriver 10 can have an inherent switch assembly.FIGS. 17A-17B illustrate one such an alternative switch assembly, wherelike numerals refer to like parts.

Referring now to FIGS. 17A-17B for this embodiment, a power trainassembly 49 as shown in FIG. 4, which includes motor 26, the outputmember 11 and/or any transmission there between, is preferably encasedin a housing 71 and made to translate axially inside the first housingportion 12. A spring 72 of adequate stiffness biases the drivetrainassembly 71 forward in the tool housing. A momentary push-button switch73 is placed in axial alignment with the drivetrain assembly 71. Whenthe tool is applied to a fastener, a bias load is applied along the axisof the tool and the drivetrain assembly 71 translates rearwardcompressing the spring and contacting the pushbutton. In an alternativeexample, the drivetrain assembly remains stationary but a collar 74surrounding the bit is made to translate axially and actuate a switch.Other arrangements for actuating the switch are also contemplated.

When the pushbutton 73 is actuated (i.e., placed in a closed state), thebattery 28 is connected via power-regulating circuits to the rotationalmotion sensor, the controller 24, and other support electronics. Withreference to FIG. 7, the controller 24 immediately turns on a bypassswitch 34 (e.g., FET). This enables the tool electronics to continuereceiving power even after the pushbutton is released. When the tool isdisengaged from the fastener, the spring 72 again biases the drivetrainassembly 71 forward and the pushbutton 73 is released. In an exemplaryembodiment, the controller 24 will remain powered for a predeterminedamount of time (e.g., 10 seconds) after the pushbutton 73 is released.During this time, the tool may be applied to the same or differentfastener without the tool being powered down. Once the pushbutton 73 hasreleased for the predetermined amount of time, the controller 24 willturn off the bypass switch 34 and power down the tool. It is preferablethat there is some delay between a desired tool shut down and poweringdown the electronics. This gives the driver circuit time to brake themotor to avoid motor coasting. In the context of the embodimentdescribed in FIG. 7, actuation of pushbutton 73 also serves to reset(i.e., set to zero) the angular position. Powering the electronics maybe controlled by the pushbutton or with a separate switch. Batterieswhich are replaceable and/or rechargeable serve as the power source inthis embodiment, although the concepts disclosed herein as alsoapplicable to corded tools.

The operational state of the tool may be conveyed to the tool operatorby a light emitting diode 35 (LED) that will be illuminated while thetool is powered-up. The LED 35 may be used to indicate other toolconditions. For example, a blinking LED 35 may indicate when a currentlevel has been exceeded or when the battery is low. In an alternativearrangement, LED 35 may be used to illuminate a work surface.

In another alternative arrangement (as shown in FIG. 21), multiple LEDsmay be used to indicate the direction and speed of tool operation. Forexample, three side-by-side LEDs 35 can be lit consecutively one at atime from left to right when the output member 11 is rotating in aclockwise direction and from right to left when output member 11 isrotating in a counterclockwise direction. The duration of illumination,or blink rate, may indicate the speed of operation, where the longereach LED is lit, the slower the operation speed. When the direction ofrotation of output member 11 is reversed, the LEDs 35 should to reflectthis transition. For example, the LEDs 35 could all be litsimultaneously for a brief period when the tool's rotation passes backthrough the starting or reference point to indicate the change. If theuser does nothing else, the LEDs 35 might turn off or return to showingbattery life or some other status. If the user continues to rotate thetool in the opposite direction, the LEDs 35 would resume consecutiveillumination and blink rate based on direction and speed of rotation.Other alternative embodiments could include more or fewer LEDs used asdescribed above.

In another alternative arrangement, the direction of rotation of outputmember 11 might be indicated by one LED arrow. The arrow may changecolor based on speed, for example, from green to yellow to orange tored. The speed could also be indicated by the arrow's blink rate.

In this embodiment, the tool may be powered up but not engaged with afastener. Accordingly, the controller may be further configured to drivethe output member only when the pushbutton switch 73 is actuated. Inother words, the output member is driven only when the tool is engagedwith a fastener and a sufficient bias force is applied to the drivetrainassembly. Control algorithm may allow for a lesser bias force when afastener is being removed. For instance, the output member may be drivenin a reverse direction when a sufficient bias load is applied to thedrivetrain assembly as described above. Once the output member beginsrotating, it will not shut off (regardless of the bias force) until someforward rotation is detected. This will allow the operator to loosen ascrew and lower the bias load applied as the screw reverses out of thematerial without having the tool shut off because of a low bias force.Other control schemes that distinguish between a forward operation and areverse operation are also contemplated by this disclosure.

Non-contacting sensing methods may also be used to control operation ofthe tool. For example, a non-contact sensor 170 may be disposed on theforward facing surface 174 of the tool adjacent to the bit 178 as shownin FIG. 17C. The non-contact sensor 170 may be used to sense when thetool is approaching, being applied to, or withdrawing from a workpiece.Optic or acoustic sensors are two exemplary types of non-contactsensors. Likewise, an inertial sensor, such as an accelerometer, can beconfigured to sense the relative position or acceleration of the tool.For example, an inertial sensor can detect linear motion of the tooltowards or away from a workpiece along the longitudinal axis of thetool. This type of motion is indicative of engaging a workpiece with thetool or removing the tool after the task is finished. These methods maybe more effective for sensing joint completion and/or determining whento turn the tool off.

Combinations of sensing methods are also contemplated by thisdisclosure. For example, one sensing method may be used for startupwhile another is used for shutdown. Methods that respond to forceapplied to the workpiece may be preferred for determining when to startup the tool, while methods that sense the state of the fastener ormovement of the tool away from the application may be preferred fordetermining when to modify tool output (e.g., shut down the tool).

Components residing in the housing of the screwdriver 10 include arotational rate sensor 22, which may be spatially separated in a radialdirection from the output member as well as a controller 24 electricallyconnected to the rotational rate sensor 22 and a motor 26 as furtherillustrated schematically in FIG. 7. A motor drive circuit 25 enablesvoltage from the battery to be applied across the motor in eitherdirection. The motor 26 in turn driveably connects through atransmission (not shown) to the output member 11. In the exemplaryembodiment, the motor drive circuit 25 is an H-bridge circuitarrangement although other arrangements are contemplated. Thescrewdriver 10 may also include a temperature sensor 31, a currentsensor 32, a tachometer 33 and/or a LED 35. Although a few primarycomponents of the screwdriver 10 are discussed herein, it is readilyunderstood that other components may be needed to construct thescrewdriver.

In an exemplary embodiment, rotational motion sensor 22 is furtherdefined as a gyroscope. The operating principle of the gyroscope isbased on the Coriolis effect. Briefly, the rotational rate sensor iscomprised of a resonating mass. When the power tool is subject torotational motion about the axis of the spindle, the resonating masswill be laterally displaced in accordance with the Coriolis effect, suchthat the lateral displacement is directly proportional to the angularrate. It is noteworthy that the resonating motion of the mass and thelateral movement of the mass occur in a plane which is orientedperpendicular to the rotational axis of the rotary member. Capacitivesensing elements are then used to detect the lateral displacement andgenerate an applicable signal indicative of the lateral displacement. Anexemplary rotational rate sensor is the ADXRS150 or ADSRS300 gyroscopedevice commercially available from Analog Devices. It is readilyunderstood that accelerometers, compasses, inertial sensors and othertypes of rotational motion sensors are contemplated by this disclosure.It is also envisioned that the sensor as well as other tool componentsmay be incorporated into a battery pack or any other removable piecesthat interface with the tool housing.

During operation, the rotational motion sensor 22 monitors rotationalmotion of the sensor with respect to the longitudinal axis of the outputmember 11. A control module implemented by the controller 24 receivesinput from the rotational motion sensor 22 and drives the motor 26 andthus the output member 11 based upon input from the rotational motionsensor 22. For example, the control module may drive the output member11 in the same direction as the detected rotational motion of the tool.As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable components that provide the described functionality; or acombination of some or all of the above, such as in a system-on-chip.The term module may include memory (shared, dedicated, or group) thatstores code executed by the processor, where code, as used above, mayinclude software, firmware, and/or microcode, and may refer to programs,routines, functions, classes, and/or objects.

Functionality for an exemplary control scheme 80 is further describedbelow in relation to FIG. 8A. During tool operation, angulardisplacement may be monitored by the controller 24 based upon inputreceived from the rotational motion sensor 22. In step 81, a starting orreference point (θ) is initialized to zero. Any subsequent angulardisplacement of the tool is then measured in relation to this reference.In an exemplary embodiment, the control scheme is implemented ascomputer executable instructions residing in a memory and executed by aprocessor of the controller 24.

At any point during operation, the user may wish to reset the startingor reference point (□). For example, the user's wrist may be rotated 40°clockwise, and the user wants to reverse the direction of the tool'soperation. Instead of rotating back through the reference point andcontinuing to rotate to the left, the user may reset the reference pointto be the current position (in this example, 40° clockwise). Anysubsequent counterclockwise rotation from the new reference point willreverse the direction of the rotation of output member 11. In the secondexemplary embodiment (as shown in FIG. 20), where holding in the triggerswitch assembly 50 is how the tool remains in a powered-up state,releasing the trigger switch assembly 50 would reset the referencepoint. In an alternate embodiment, pressing the dedicated zero button210 (as shown in FIG. 21) would reset the reference point. Personsskilled in the art will recognize that other implementations can beenvisioned, such as requiring the zero button 210 to be pressed and heldfor a short period of time in order to prevent accidental zeroing.

Angular displacement of the tool is then monitored at step 82. In theexemplary embodiment, the angular displacement is derived from the rateof angular displacement over time or angular velocity (ω_(TOOL)) asprovided by the gyroscope. While the rotational rate sensor describedabove is presently preferred for determining angular displacement of thetool, it is readily understood that this disclosure is not limited tothis type of sensor. On the contrary, angular displacement may bederived in other manners and/or from other types of sensors. It is alsonoted that the signal from any rotational rate sensor can be filtered inthe analog domain with discrete electrical components and/or digitallywith software filters.

In this proposed control scheme, the motor is driven at differentrotational speeds depending upon the amount of rotation. For example,the angular displacement is compared at 84 to an upper threshold. Whenthe angular displacement exceeds an upper threshold θ_(UT) (e.g., 30° ofrotation), then the motor is driven at full speed as indicated at 85.The angular displacement is also compared at 86 to a lower threshold.When the angular displacement is less than the upper threshold butexceeds a lower threshold θ_(LT) (e.g., 5° of rotation), then the motoris driven at half speed as indicated at 87. It is readily understoodthat the control scheme may employ more or less displacement thresholdsas well as drive the motor at other speeds.

Angular displacement continues to be monitored at step 82. Subsequentcontrol decisions are based on the absolute angular displacement inrelation to the starting point as shown at 83. When the angulardisplacement of the tool remains above the applicable threshold, thenthe operating speed of the motor is maintained. In this way, continuousoperation of the tool is maintained until the tool is returned to itsoriginal position. In the exemplary embodiment, returning the tool toits original position means that the user returns the tool to within 10°to 15° of the original position, for example. This creates a rangearound the reference point that allows for a small margin of user error.The user is not required to find the exact reference point that was set.On the other hand, when the tool operator rotates the tool in theopposite direction and angular displacement of the tool drops below (isless than) the lower threshold, then the output of the tool is modifiedat 190. In an exemplary embodiment, the voltage applied to the motor isdiscontinued at 190, thereby terminating operation of the tool. In analternative embodiment, the speed at which the motor is driven isreduced to some minimal level that allows for spindle rotation at noload. Other techniques for modifying output of the tool are alsoenvisioned. Threshold values may include hysteresis; that is, the lowerthreshold is set at one value (e.g. six degrees) for turning on themotor but set at a different value (e.g., four degrees) for turning offthe motor, for example. It is also to be understood that only therelevant steps of the methodology are discussed in relation to FIG. 8A,but that other functionality may be needed to control and manage theoverall operation of the system.

A variant of this control scheme 80′ is shown in FIGS. 8B. When theangular displacement is less than the upper threshold but exceeds alower threshold θ_(LT) (e.g., 5° of rotation), then the motor speed maybe set generally as a function of the angular displacement as indicatedat 87′. More specifically, the motor speed may be set proportional tothe full speed. In this example, the motor speed is derived from alinear function. It is also noted that more complex functions, such asquadratic, exponential or logarithmic functions, may be used to controlmotor speed. In another embodiment, the motor speed could beproportional to the displacement, velocity, acceleration, or acombination thereof (as shown in FIG. 8B, step 87′).

In either control scheme described above, direction of tool rotation maybe used to control the rotational direction of the output member. Inother words, a clockwise rotation of the tool results in a clockwiserotation of the output member, and a counterclockwise rotation of thetool results in a counterclockwise rotation of the output member.Alternatively, the tool may be configured with a switch that enables theoperator to select the rotational direction of the output member.

Persons skilled in the art will recognize that rotational motion sensor22 can be used in diverse ways. For example, the motion sensor 22 can beused to detect fault conditions and terminate operation. One such schemeis shown in FIG. 8C where, if the angular displacement is larger thanthe upper threshold θ_(U) (step 86), it could be advantageous to checkwhether the angular displacement exceeds on a second upper thresholdθ_(OT) (step 88). If such threshold is exceeded, then operation ofscrewdriver 10 can be terminated (step 89). Such arrangement isimportant in tools that should not be inverted or put in certainorientations. Examples of such tools include table saws, power mowers,etc.

Similarly, operation of screwdriver 10 can be terminated if motionsensor 22 detects a sudden acceleration, such as when a tool is dropped.

Alternatively, the control schemes in FIGS. 8A-8C can be modified bymonitoring angular velocity of output member 11 about the longitudinalaxis 8 instead of angular displacement. In other words, when the angularvelocity of rotation exceeds an upper threshold, such as 100°/second,then the motor is driven at full speed, whereas if the angular velocityis lower than the upper threshold but exceeds a lower threshold, such as50°/second, then the motor is driven at half speed.

Alternatively, the control schemes shown in FIGS. 8A-8C can be modifiedby monitoring angular acceleration instead of angular velocity. In otherwords, when the angular acceleration of rotation exceeds an upperthreshold, such as 100°/second per second, then the motor is driven atfull speed, whereas if the angular acceleration is lower than the upperthreshold but exceeds a lower threshold, such as 50°/second per second,then the motor is driven at half speed. Alternatively, a combination ofdisplacement, velocity, and/or acceleration could determine the controlscheme.

With reference to FIG. 18, a ratcheting control scheme 60 is alsocontemplated by this disclosure. During tool operation, the controllermonitors angular displacement of the tool at 61 based upon inputreceived from the rotational motion sensor 22. From angulardisplacement, the controller is able to determine the direction of thedisplacement at 62 and drive the motor 26 to simulate a ratchet functionas further described below.

In this proposed control scheme, the controller must also receive anindication from the operator at 63 as to which direction the operatordesires to ratchet. In an exemplary embodiment, the screwdriver 10 maybe configured with a switch that enables the operator to select betweenforward and reverse ratchet directions. Other input mechanisms are alsocontemplated.

When the forward ratchet direction is selected by the operator, thecontroller drives the motor in the following manner. When the operatorrotates the tool clockwise, the output member is driven at a higherratio than the rotation experienced by the tool. For example, the outputmember may be driven one or more full revolutions for each quarter turnof the tool by the operator. In other words, the output member isrotated at a ratio greater than one when the direction of rotationalmotion is the same as a user selected ratcheting direction as indicatedat 65. It may not be necessary for the user to select a ratchetdirection. Rather the control may make a ratcheting direction decisionbased on a parameter, for example, an initial rotation direction isassumed the desired forward direction.

On the other hand, when the operator rotates the tool counter clockwise,the output member is driven at a one-to-one ratio. Thus the outputmember is rotated at a ratio equal to one when the direction rotationalmotion is the opposite the user selected ratcheting direction asindicated at 67. In the case of the screwdriver, the bit and screw wouldremain stationary as the user twists the tool backward to prepare forthe next forward turn, thereby mimicking a ratcheting function.

The control schemes set forth above can be further enhanced by the useof multiple control profiles. Depending on the application, the tooloperator may prefer a control curve that gives more speed or morecontrol. FIG. 9 illustrates three exemplary control curves. Curve A is alinear control curve in which there is a large variable control region.If the user does not need fine control for the application and simplywants to run an application as fast as possible, the user would prefercurve B. In this curve, the tool output ramps up and obtains full outputquickly. If the user is running a delicate application, such as seatinga brass screw, the user would prefer curve C. In this curve, obtainingimmediate power is sacrificed to give the user a larger control region.In the first part of the curve, output power changes slowly; whereas,the output power changes more quickly in the second part of the curve.Although three curves are illustrated, the tool may be programmed withtwo or more control curves.

In one embodiment, the tool operator may select one of a set number ofcontrol curves directly with an input switch. In this case, thecontroller applies the control curve indicated by the input switch untilthe tool operator selects a different control curve.

In an alternative embodiment, the controller of the tool can select anapplicable control curve based on an input control variable (ICV) andits derivative. Examples of ICVs include displacement, velocity, andacceleration. The motor speed from the selected curve may be determinedby either the same or some other variable. For example, the controllermay select the control curve based on distance a trigger has traveledand the speed at which the user actuates the trigger switch. In thisexample, the selection of the control curve is not made until thetrigger has traveled some predetermined distance (e.g., 5% of the travelrange as shown in FIG. 9A) as measured from a starting position.

Once the trigger has traveled the requisite distance, the controllercomputes the speed of the trigger and selects a control curve from agroup of control curves based on the computed speed. If the user simplywants to drive the motor as quick as possible, the user will tend topull the trigger quickly. For this reason, if the speed of triggerexceeds some upper speed threshold, the controller infers that the userwants to run the motor as fast as possible and selects an applicablecontrol curve (e.g., Curve B in FIG. 9A). If the user is working on adelicate application and requires more control, the user will tend topull the trigger more slowly. Accordingly, if the speed of trigger isbelow some lower speed threshold, the controller infers the user desiresmore control and selects a different control curve (e.g., Curve C inFIG. 9A). If the speed of the trigger falls between the upper and lowerthresholds, the controller may select another control curve (e.g., CurveA in FIG. 9A). Curve selection could be (but is not limited to being)performed with every new trigger pull, so the user can punch the triggerto run the screw down, release, and obtain fine seating control with thenext slower trigger pull.

The controller then controls the motor speed in accordance with theselected control curve. In the example above, the distance travelled bythe trigger correlates to a percent output power. Based on the triggerdistance, the controller will drive the motor at the correspondingpercent output in accordance with the selected control curve. It isnoted that this output could be motor pulse width modulation, as in anopen loop motor control system, or it could be motor speed directly, asin a closed loop motor control system.

In another example, the controller may select the control curve based ona different input control variable, such as the angular distance thetool has been rotated from a starting point and its derivative, i.e.,the angular velocity at which the tool is being rotated. Similar totrigger speed, the controller can infer that the user wants to run themotor as fast as possible when the tool is rotated quickly and inferthat the user wants to run the motor slower when the tool is beingrotated slowly. Thus, the controller can select and apply a controlcurve in the manner set forth above. In this example, the percentage ofthe input control variable is computed in relation to a predefined rangeof expected rotation (e.g., +/−180 degrees). Selecting an applicablecontrol curve based on another type of input control variable land itsderivative is also contemplated by this disclosure.

It may be beneficial to monitor the input control variable and selectcontrol curves at different points during tool operation. For example,the controller may compute trigger speed and select a suitable controlcurve after the trigger has been released or otherwise begins travelingtowards its starting position. FIG. 9B illustrates three exemplarycontrol curves that can be employed during such a back-off condition.Curve D is a typical back off curve which mimics the typical ramp upcurve, such as Curve A. In this curve, the user passes through the fullrange of analog control before returning to trigger starting position.Curve E is an alternative curve for faster shutoff. If the trigger isreleased quickly, the controller infers that the user simply wants toshut the tool off and allows the user to bypass most of the variablespeed region. If the user backs off slowly, the controller infers thatthe user desires to enter the variable speed region. In this case, thecontroller may select and apply Curve F to allow the user better finishcontrol, as would be needed to seat a screw. It is envisioned that thecontroller may monitor the input control variable and select anapplicable control curve based on other types of triggering events whichoccur during tool operation.

Ramp up curves may be combined with back off curves to form a singleselectable curve as shown in FIG. 9C. In an exemplary application, theuser wishes to use the tool to drive a long machine screw and thusselects the applicable control curves using the input switch asdiscussed above. When the user pulls the trigger, the controller appliesCurve B to obtain full tool output quickly. When the user has almostfinished running down the screw, the user releases the trigger and thecontroller applies Curve F, thereby giving the user more control and theability to seat the screw to the desired tightness.

Selection of control curves may be based on the input control variablein combination with other tool parameters. For example, the controllermay monitor output torque using known techniques such as sensing currentdraw. With reference to FIG. 9D, the controller has sensed a slowtrigger release, thereby indicating the user desires variable speed forfinish control. If the controller further senses that output torque ishigh, the controller can infer that the user needs more output power tokeep the fastener moving (e.g., a wood screw application). In this case,the controller selects Curve G, where the control region is shiftedupward to obtain a usable torque. On the other hand, if the controllersenses that output torque is low, the controller can infer thatadditional output power is not needed (e.g., a machine screwapplication) and thus select Curve H. Likewise, the controller mayselect from amongst different control curves at tool startup based onthe sensed torque. Tool parameters other than torque may also be used toselect a suitable control curve.

Selection of control curves can also be based on a second derivative ofthe input control variable. In an exemplary embodiment, the controllercan continually compute the acceleration of the trigger. When theacceleration exceeds some threshold, the controller may select adifferent control curve. This approach is especially useful if the toolhas already determined a ramp up or back off curve but the user desiresto change behavior mid curve. For example, the user has pulled thetrigger slowly to allow a screw to gain engagement with a thread. Onceengaged, the user punches the trigger to obtain full output. Since thetool always monitors trigger acceleration, the tool senses that the useris finished with variable speed control and quickly sends the tool intofull output as shown in FIG. 9E.

Again, trigger input is used as an example in this scenario, but itshould be noted that any user input control, such as a gesture, could beused as the input control variable. For example, sensor 22 can detectwhen the user shakes a tool to toggle between control curves or evenoperation modes. For example, a user can shake a sander to togglebetween a rotary mode and a random orbit mode. In the examples set forthabove, the controller controls the motor speed in accordance with thesame input control variable as is used to select the control curve. Itis envisioned that the controller may control the motor speed with aninput control variable that differs from the input control variable usedto select the control curve. For example, motor speed may be set basedon displacement of the trigger; whereas, the control curve is selectedin accordance with the velocity at which the trigger is actuated.

Referring to FIG. 7, the screwdriver 10 includes a current sensor 32 todetect current being delivered to the motor 26. It is disadvantageousfor the motor of the tool to run at high current levels for a prolongedperiod of time. High current levels are typically indicative of hightorque output. When the sensed current exceeds some predefinedthreshold, the controller is configured to modify tool output (e.g.,shut down the tool) to prevent damage and signal to the operator thatmanually applied rotation may be required to continue advancing thefastener and complete the task. The tool may be further equipped with aspindle lock. In this scenario, the operator may actuate the spindlelock, thereby locking the spindle in fixed relation to the tool housing.This causes the tool to function like a manual screwdriver.

For such inertia-controlled tools, there may be no indication to theuser that the tool is operational, for example, when the user depressesthe trigger switch assembly 50 but does not rotate the tool.Accordingly, the screwdriver 10 may be further configured to provide auser-perceptible output when the tool is operational. Providing the userwith haptic feedback is one example of a user-perceptible output. Themotor driven circuit 25 may be configured as an H-bridge circuit asnoted above and in FIG. 7. The H-bridge circuit is used to selectivelyopen and close pairs of field effect transistors (FETs) to change thecurrent flow direction and therefore the rotational direction of themotor. By quickly transitioning back and forth between forward andreverse, the motor can be used to generate a vibration perceptible tothe tool operator. The frequency of a vibration is dictated by the timespan for one period and the magnitude of a vibration is dictated by theratio of on time to off time as shown in FIG. 10. Other schemes forvibrating the tool also fall within the broader aspects of thisdisclosure.

Within the control schemes presented in FIGS. 8A-8C, the H-bridgecircuit 25 (as seen in FIG. 7) may be driven in the manner describedabove before the angular displacement of the tool reaches the lowerthreshold. Consequently, the user is provided with haptic feedback whenthe spindle is not rotating. It is also envisioned that user may beprovided haptic feedback while the spindle is rotating. For example, thepositive and negative voltage may be applied to the motor with animbalance between the voltages such that the motor will advance ineither a forward or reverse direction while still vibrating the tool. Itis understood that haptic feedback is merely one example of aperceptible output and other types of outputs also are contemplated bythis disclosure.

Vibrations having differing frequencies and/or differing magnitudes canalso be used to communicate different operational states to the user.For example, the magnitude of the pulses can be changed proportionallyto speed to help convey where in a variable-speed range the tool isoperating. So as not to limit the total tool power, this type offeedback may be dropped out beyond some variable speed limit (e.g., 70%of maximum speed). In another example, the vibrations may be used towarn the operator of a hazardous tool condition. Lastly, the hapticfeedback can be coupled with other perceptible indicators to helpcommunicate the state of the tool to the operator. For instance, a lighton the tool may be illuminated concurrently with the haptic feedback toindicate a particular state.

Additionally, haptic feedback can be used to indicate that the outputmember has rotated 360°, or that a particular desired torque setting hasbeen achieved.

In another aspect of this invention, an automated method is provided forcalibrating a gyroscope residing in the screwdriver 10. Gyroscopestypically output a sensed-analog voltage (Vsense) that is indicative ofthe rate of rotation. Rate of rotation can be determined by comparingthe sensed voltage to a reference voltage (e.g.,rate=(Vsense-Vref)/scale factor). With some gyroscopes, this referencevoltage is output directly by the gyroscope. In other gyroscopes, thisreference voltage is a predetermined level (i.e., gyroscope supplyvoltage/2) that is set as a constant in the controller. When the sensedvoltage is not equal to the reference voltage, rotational motion isdetected. When the sensed voltage is equal to the reference voltage, nomotion is occurring. In practice, there is an offset error (ZRO) betweenthe two voltages (i.e., ZRO=Vsense-Vref). This offset error can becaused by different variants, such as mechanical stress on a gyroscopeafter mounting to a PCT or an offset error in the measuring equipment.The offset error is unique to each gyroscope but should remain constantover time. For this reason, calibration is often performed after a toolis assembled to determine the offset error. The offset error can bestored in memory and used when calculating the rotational rate (i.e.,rate−(Vsense-Vref-ZRO/scale).

Due to changes in environmental conditions, it may become necessary torecalibrate the tool during the course of tool use. Therefore, it isdesirable for the tool to be able to recalibrate itself in the field.FIG. 11 illustrates an exemplary method for calibrating the offset errorof the gyroscope in the tool. In an exemplary embodiment, the method isimplemented by computer-executable instructions executed by a processorof the controller 24 in the tool.

First, the calibration procedure must occur when the tool is stationary.This is likely to occur once an operation is complete and/or the tool isbeing powered down. Upon completing an operation, the tool will remainpowered on for a predetermined amount of time. During this time period,the calibration procedure is preferably executed. It is understood thatthe calibration procedure may be executed at other times when the toolis or is likely to be stationary. For example, the first derivative ofthe sensed voltage measure may be analyzed to determine when the tool isstationary.

The calibration procedure begins with a measure of the offset error asindicated at 114. After the offset error is measured, it is compared toa running average of preceding offset error measurements (ZROavg). Therunning average may be initially set to the current calibration valuefor the offset error. The measured offset error is compared at 115 to apredefined error threshold. If the absolute difference between themeasured offset error and the running average is less than or equal tothe predefined offset error threshold, the measured offset error may beused to compute a newly-calibrated offset error. More specifically, themeasurement counter (calCount) may be incremented at 116 and themeasured offset error is added to an accumulator (ZROaccum) at 117. Therunning average is then computed at 118 by dividing the accumulator bythe counter. A running average is one exemplary way to compute thenewly-calibrated offset error.

Next, a determination is made as to whether the tool is stationaryduring the measurement cycle. If the offset error measurements remainconstant or nearly constant over some period of time (e.g., 4 seconds)as determined at 119, the tool is presumed to be stationary. Before thistime period is reached, additional measurements of the offset error aretaken and added to the running average so long as the difference betweeneach offset error measurement and the running average is less than theoffset error threshold. Once the time period is reached, the runningaverage is deemed to be a correct measurement for the offset error. Therunning average can be stored in memory at 121 as the newly-calibratedoffset error and subsequently used by the controller during thecalculations of the rotational rate.

When the absolute difference between the measured offset error and therunning average exceeds the predefined offset error threshold, the toolmust be rotating. In this case, the accumulator and measurement counterare reset as indicated at steps 126 and 127. The calibration proceduremay continue to execute until the tool is powered down or some othertrigger ends the procedure.

To prevent sudden erroneous calibrations, the tool may employ alonger-term calibration scheme. The method set forth above determineswhether or not there is a need to alter the calibration value. Thelonger-term calibration scheme would use a small amount of time (e.g.,0.25 s) to perform short-term calibrations, since errors would not becritical if no rotational motion is sensed in the time period. Theaveraged ZRO would be compared to the current calibration value. If theaveraged ZRO is greater than the current calibration value, thecontroller would raise the current calibration value. If the averagedZRO is less than the current calibration value, the controller wouldlower the current calibration value. This adjustment could either beincremental or proportional to the difference between the averaged valueand the current value.

Due to transmission backlash, the tool operator may experience anundesired oscillatory state under certain conditions. While the gears ofa transmission move through the backlash, the motor spins quickly, andthe user will experience like reactionary torque. As soon as thebacklash is taken up, the motor suddenly experiences an increase in loadas the gears tighten, and the user will quickly feel a strongreactionary torque as the motor slows down. This reactionary torque canbe strong enough to cause the tool to rotate in the opposite directionas the output spindle. This effect is increased with a spindle locksystem. The space between the forward and reverse spindle locks actssimilarly to the space between gears, adding even more backlash into thesystem. The greater the backlash, the greater amount of time the motorhas to run at a higher speed. The higher a speed the motor achievesbefore engaging the output spindle, the greater the reactionary torque,and the greater the chance that the body of the tool will spin in theopposite direction.

While a tool body's uncontrolled spinning may not have a large effect ontool operation for trigger-controlled tools, it may have a prominent anddetrimental effect for rotation-controlled tools. If the user controlstool output speed through the tool-body rotation, any undesired motionof the tool body could cause an undesired output speed. In the followingscenario, it can even create an oscillation effect. The user rotates thetool clockwise in an attempt to drive a screw. If there is a greatamount of backlash, the motor speed will increase rapidly until thebacklash is taken up. If the user's grip is too relaxed at this point,the tool will spin uncontrolled in the counterclockwise direction. Ifthe tool passes the zero rotation point and enters into negativerotation, the motor will reverse direction and spin counterclockwise.The backlash will again be taken up, eventually causing the tool body tospin uncontrolled in the clockwise direction. This oscillation oroscillatory state may continue until tool operation ceases.

FIG. 15 depicts an exemplary method of preventing such an oscillatorystate in the screwdriver 10. For illustration purposes, the method workscooperatively with the control scheme described in relation to FIG. 8A.It is understood that the method can be adapted to work with othercontrol schemes, including those set forth above. In an exemplaryembodiment, the method is implemented by controller 24 in the tool.

Rotational direction of the output spindle is dictated by the angulardisplacement of the tool as discussed above. For example, a clockwiserotation of the tool results in clockwise rotation of the output member.However, the onset of an oscillatory state may be indicated when toolrotation occurs for less than a predetermined amount of time beforebeing rotated in the opposing direction. Therefore, upon detectingrotation of the tool, a time is initiated at 102. The timer accrues theamount of time the output member has been rotating in a given direction.Rotational motion of the tool and its direction are continually beingmonitored as indicated at 103.

When the tool is rotated in the opposite direction, the method comparesthe value of the timer to a predefined threshold (e.g., 50 ms) at 104.If the value of the timer is less than the threshold, the onset of anoscillatory state may be occurring. In an exemplary embodiment, theoscillatory state is confirmed by detecting two oscillations although itmay be presumed after a single oscillation. Thus, a flag is set at 105to indicate the occurrence of a first oscillation. If the value of thetimer exceeds the threshold, the change in rotational direction ispresumed to be intended by the operator and thus the tool is not in anoscillating state. In either case, the timer value is reset andmonitoring continues.

In an oscillatory state, the rotational direction of the tool will againchange as detected at 103. In this scenario, the value of the timer isless than the threshold and the flag is set to indicate the precedingoccurrence of the first oscillation. Accordingly, a corrective actionmay be initiated as indicated at 107. In an exemplary embodiment, thetool may be shut down for a short period of time (e.g., ¼ second),thereby enabling the user to regain control of the tool before operationis resumed. Other types of corrective actions are also contemplated bythis disclosure. It is envisioned that the corrective action may beinitiated after a single oscillation or some other specific number ofoscillations exceeding two. Likewise, other techniques for detecting anoscillatory state fall within the broader aspects of this disclosure.

In another arrangement, the tool may be configured with self-lockingplanetary gear set 90 disposed between the output member 11 and a driveshaft 91 of the motor 26. The self-locking gear set could include anyplanetary gear set which limits the ability to drive the sun gearthrough the ring gear and/or limits the ability of the spindle toreverse. This limiting feature could be inherent in the planetary gearset or it could be some added feature such as a sprag clutch or a oneway clutch. Referring to FIGS. 19A and 19B, one inherent method to limitthe ability of a ring gear to back drive a sun gear 92 is to add anadditional ring gear 93 as the output of the planetary gear set 94 andfix the first ring gear 95. By fixing the first ring gear 95, power istransferred through the sun gear 92 into the planetary gear set 94 intothe second (unfixed, out) ring gear 93.

When torque is applied back through the output ring gear 93 into theplanetary gear set 94, the internal gear teeth on the output ring gearare forced into engagement with the corresponding teeth on the planetarygear set 94. The teeth on the planetary gear set 94 are then forced intoengagement with the corresponding teeth on the fixed ring gear. Whenthis happens, the forces on the planetary gears' teeth are balanced bythe forces acting through the output ring gear 93 and the equal andopposite forces acting through the fixed ring gear 95 as seen in FIG.19B. When the forces are balanced, the planetary gear is fixed and doesnot move. This locks the planetary gear set and prevents torque frombeing applied to the sun gear. Other arrangements for the self-lockinggear set are also contemplated by this disclosure.

The advantage of having a self-locking planetary gear set is that whenthe motor is bogged down at high torque levels during twistingoperations such as, but not limited to, threaded fasteners, the tooloperator can overcome the torque by twisting the tool. This extra torqueapplied to the application from the tool operator is counteracted by theforces within the self-locking planetary gear set, and the motor doesnot back drive. This allows the tool operator to apply additional torqueto the application.

In this arrangement, when the sensed current exceeds some predefinedthreshold, the controller may be configured to drive the motor at someminimal level that allows for spindle rotation at no load. This avoidsstressing the electronics in a stall condition but would allow forratcheting at stall. The self-locking planetary gears would still allowthe user to override stall torque manually. Conversely, when the userturns the tool in the reverse direction to wind up for the next forwardturn, the spindle rotation would advance the bit locked in thescrewhead, thereby counteracting the user's reverse tool rotation.

With reference to FIG. 20, a second exemplary power screwdriver isindicated generally by reference number 10′. This embodiment allows theuser to hold the screwdriver 10′ in the palm of the user's hand andactuate the trigger switch assembly 50′ with the palm of the user'shand, most preferably the area of the palm that forms the base of theuser's thumb. In this embodiment, the tool operator actuates the triggerswitch assembly 50′ to initiate tool operation. Given the orientation ofthe screwdriver 10′ in the palm of the user's hand, it should berecognized that the trigger switch assembly 50′ is actuated and remainsdepressed just by holding the screwdriver 10′. This allows for naturaland intuitive use, where the user can simply hold the screwdriver 10′and turn it.

With reference to FIGS. 5A-5C and 20, the trigger switch assembly 50′ issubstantially similar to the trigger switch assembly 50. The triggerswitch assembly 50′ is comprised primarily of an elongated casing 52that houses at least one momentary switch 53 and a biasing member 54,such as a spring. The elongated casing 52 is movably coupled to housing200 in such a way that allows it to translate and/or pivot about anypoint of contact by the operator. For example, if the tool operatorpresses near the top or bottom of the elongated casing 52, the triggerswitch assembly 50′ pivots as shown in FIGS. 5A and 5B, respectively. Ifthe tool operator presses near the middle of the elongated casing 52,the trigger switch assembly 50′ is translated inward towards the toolbody as shown in FIG. 5C. In any case, the force applied to theelongated casing 52 by the operator will depress at least one of theswitches from an OFF position to an ON position. If there are two ormore switches 53, the switches 53 are arranged electrically in parallelwith each other (as shown in FIG. 7) such that only one of the switchesneeds to be actuated to power up the tool. When the operator releasesthe trigger, the biasing member 54 biases the elongated casing 52 awayfrom the tool, thereby returning each of the switches to an OFFposition. The elongated shape of the casing helps the operator toactuate the switch from different grip positions. It is envisioned thatthe trigger switch assembly 50′ may be comprised of more than twoswitches 53 and/or more than one biasing member 54 as shown in FIGS.6A-6C. This embodiment otherwise functions as described for the previousembodiment.

With reference to FIG. 21, a third exemplary power screwdriver isindicated generally by reference number 10″. In this embodiment, thetool operator actuates the trigger switch assembly 50″ with the user'sindex finger to power up the screwdriver 10″. The trigger switchassembly 50″ functions as an ON/OFF switch. Once the user presses andreleases the trigger switch assembly 50″, the screwdriver 10″ is in anON state (i.e., the battery is connected to the controller and otherelectronic components). Rotational motion is detected and acted upononly when the tool is powered up. When the operator places the switch inan OFF position, the tool is powered down and is no longer operational.The screwdriver 10″ remains in the ON state until the user turns it offby pressing and releasing the trigger switch assembly 50″ again. It isalso contemplated that the screwdriver 10″ will automatically shut offafter a period of inactivity, and the trigger switch assembly 50″ may beimplemented in other ways.

Output member 11 rotates around longitudinal axis 8′ based on angulardisplacement as described above. In other words, the user rotates thescrewdriver 10″ to drive output member 11. In this third embodiment, azero button 210 allows the user to reset the starting or reference pointas previously described.

The tool may be further configured with a reaming tool 214 disposedbetween the second housing portion 14 and the output member 11. Forexample, a user may wish to refine a hole drilled using the tool orremove burrs from the cut end of a piece of conduit. This embodiment hastwo modes of operation: the motor 26 either drives the output member 11or the reaming tool 214. In one arrangement, the mode is selectedmanually by the user as shown in FIGS. 22A-22B and described below. Inanother arrangement, the mode is selected by applying either the outputmember 11 or the reaming tool 214 to a workpiece in order to usescrewdriver 10″ as a screwdriver or a reamer, respectively, as shown inFIGS. 23A-23B and described below. Other means for selecting the mode ofoperation are also contemplated by this disclosure.

Other reaming tool variations are contemplated. In an alternativeembodiment, the reaming tool would oscillate. For example, the user'swrist remains rotated clockwise, and the reaming tool rotates in aclockwise direction for a short time period, reverses direction for ashort time period, repeating until operation is terminated. In anotheralternative embodiment, the reaming tool would have a pulse mode. If thedrive signal is pulsed, a spike in the torque output might facilitateovercoming a burr. In still another alternative embodiment, the powertool could have multiple gears associated with it. At lower speeds,higher torque could be achieved while at higher speeds, lower torquewould be sufficient for driving screws, for example.

FIGS. 22A-22B show an exemplary clutch mechanism for selectivelyengaging the reaming tool 214 (to operate screwdriver 10″ as a reamer)or the output member 11 (to operate screwdriver 10″ as a screwdriver).It is to be understood that the representation of the reaming tool 214in FIGS. 22A-22B has been simplified from its depiction in FIG. 21 inorder to more clearly convey the mode switching.

In this exemplary embodiment, the user rotates a collar 240 between twopositions to select the mode of operation. It should be understood thatthis collar could also be implemented to translate between the twopositions while remaining rotationally fixed. The collar 240 is attachedto a grounding ring 228. When the grounding ring 228 is in the rearwardposition as shown in FIG. 22A, the grounding ring 228 engages a planetcarrier 236 and prevents it from rotating. In this configuration, themotor drives the planets 237 to rotate about the pins of the planetcarrier 236, causing the ring gear 232 to rotate. This drives thereaming tool 214 while the output member 11 remains fixed, and as such,screwdriver 10″ operates as in reamer mode. When the grounding ring 228is in the forward position as shown in FIG. 22B, the planet carrier 236is free to rotate, and the ring gear 232 is fixed. In thisconfiguration, the motor drives the planets 237 which in turn drives theoutput member 11, and as such, screwdriver 10″ operates in screwdrivermode. It is envisioned that in an alternative embodiment, the ring gear232 and the planet carrier 236 may be fixed to one another and free torotate at the same time.

FIGS. 23A and 23B illustrate another exemplary clutch mechanism forselecting the mode of operation. In this embodiment, a dog type clutch238 is used to selectively engage the reaming tool 214. It is to beunderstood that the representation of the reaming tool 214 in FIGS.23A-23B has been simplified from its depiction in FIG. 21 in order tomore clearly convey the mode switching.

In this arrangement, screwdriver 10″ operates as a screwdriver as shownin FIG. 23A unless the user applies the reaming tool 214 to a workpiece230. If no force is applied to the reaming tool, the dog clutch 238 isnot engaged, and the output member 11 is free to rotate. To operatescrewdriver 10″ as a reamer, the user applies the reaming tool 214 to aworkpiece 230. This bias load applies a force to the compression springs234, as shown in FIG. 23B. This engages the dog clutch 238, which causesthe reaming tool 214 to rotate with the output member 11. Thisembodiment otherwise functions the same as the other embodimentsdiscussed above.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

Example embodiments are provided so that this disclosure will bethorough and will fully convey the scope to those who are skilled in theart. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

1. A method for operating a power tool having an output shaft, comprising: receiving an input control variable from an input unit; determining a derivative of the input control variable; selecting one of a plurality of control profiles based on the control input variable and the derivative, each control profile correlating the control input variable of the input unit to a rotational speed at which to drive the output shaft; and driving the output shaft at a rotational speed in accordance with the selected control profile.
 2. The method of claim 1 further comprising: selecting a first control profile from the plurality of control profiles when the derivative of the control input variable is above a first threshold and selecting a second control profile from the plurality of control profiles when the derivative of the control input variable is below the first threshold, where the first control profile differs from the second control profile.
 3. The method of claim 2, wherein the first control profile designates maximum rotational speed of the output shaft for a predetermined range of the corresponding control input variable and the second control profile designates a linear control relationship between the rotational speed of the output shaft and the corresponding control input variable.
 4. The method of claim 3, further comprising selecting a third control profile from the plurality of control profiles when the variable of the control input variable is below a second threshold below the first threshold, wherein the third control profile designates a control curve comprising a first linear curve corresponding to a first range of the control input variables and a second linear curve steeper than the first linear curve and corresponding to a second range of control input variables.
 5. The method of claim 1, wherein the input unit comprises a trigger switch and the control input variable comprises one of a displacement, velocity, or acceleration of the trigger switch.
 6. The method of claim 1, wherein control input variable comprises a displacement of the input unit and the derivative of the control input variable comprises a speed at which the input unit is actuated.
 7. The method of claim 1, wherein the input unit comprises a rotational motion sensor disposed in the power tool and configured to measure rotational motion of the power tool about an axis aligned substantially parallel with a longitudinal axis of the output shaft.
 8. The method of claim 7, wherein the control input variable comprises an angular displacement of the tool about the axis and the derivative comprises an angular velocity of the tool about the axis.
 9. The method of claim 8, further comprising determining the angular displacement of the tool about the axis in relation to a reference position and driving the output shaft at a rotational speed that correlates to the angular displacement of the tool from the reference position based on the selected control profile.
 10. The method of claim 9, further comprising resetting the reference position to zero in response to an input command from an operator of the tool.
 11. A power tool comprising: a housing; an output member configured to rotate about a longitudinal axis; a motor contained in the housing and driveably connected to the output member to impart rotary motion thereto; an input unit configured to output an input control variable in response to a user action; and a controller in the housing configured to calculate a derivative of the input control variable, select one of a plurality of control profiles based on the control input variable and the derivative, and drive the output shaft via the motor at a rotational speed in accordance with the selected control profile, wherein each control profile correlating the control input variable of the input unit to a rotational speed at which to drive the output shaft.
 12. The power tool of claim 11, wherein the controller is configured to select a first control profile from the plurality of control profiles when the derivative of the control input variable is above a first threshold and select a second control profile from the plurality of control profiles when the derivative of the control input variable is below the first threshold, where the first control profile differs from the second control profile.
 13. The power tool of claim 12, wherein the first control profile designates maximum rotational speed of the output shaft for a predetermined range of the corresponding control input variable and the second control profile designates a linear control relationship between the rotational speed of the output shaft and the corresponding control input variable.
 14. The power tool of claim 13, wherein the controller is further configured to select a third control profile from the plurality of control profiles when the variable of the control input variable is below a second threshold below the first threshold, wherein the third control profile designates a control curve comprising a first linear curve corresponding to a first range of the control input variables and a second linear curve steeper than the first linear curve and corresponding to a second range of control input variables.
 15. The power tool of claim 11, wherein the input unit comprises a trigger switch and the control input variable comprises one of a displacement, velocity, or acceleration of the trigger switch.
 16. The power tool of claim 11, wherein control input variable comprises a displacement of the input unit and the derivative of the control input variable comprises a speed at which the input unit is actuated.
 17. The power tool of claim 11, wherein the input unit comprises a rotational motion sensor disposed in the power tool and configured to measure rotational motion of the power tool about an axis aligned substantially parallel with a longitudinal axis of the output shaft.
 18. The power tool of claim 17, wherein the control input variable comprises an angular displacement of the tool about the axis and the derivative comprises an angular velocity of the tool about the axis.
 19. The power tool of claim 18, wherein the controller is configured to determine the angular displacement of the tool about the axis in relation to a reference position and driving the output shaft at a rotational speed that correlates to the angular displacement of the tool from the reference position based on the selected control profile.
 20. The power tool of claim 19, wherein the controller is configured to reset the reference position to zero in response to an input command from an operator of the tool. 